This invention relates to laminates having one layer of an olefinic unsaturation containing polymer and a second layer containing an active hydrogen containing polymer. The invention also relates to processes for the preparation of such laminates.
Due to the different chemical nature of polymers having olefinic unsaturation, such as rubber, and polymers having active hydrogen atoms, such as polyurethanes, it is difficult to form laminates from such polymers. One difference is the difference in surface energy of the polymers with the olefinic unsaturation containing polymers having a low surface energy and the active hydrogen containing polymers having a high surface energy. For instance, it is desirable to improve the performance of rubber based structures, such as tires, by bonding an elastomeric layer such as a polyurethane layer to the rubber layer. Unfortunately there are no elegant means for doing this.
What is needed is an adhesive which can bond a layer of an olefin containing polymer, such as rubber, to a layer of an active hydrogen containing polymer, such as a polyurethane. What is also needed is a process for bonding such layers together. What is needed is a laminate having a layer of an olefin containing polymer, such as rubber, and a layer of an active hydrogen containing polymer, such as a polyurethane.
The invention is a laminate structure comprising two or more layers of one or both of
a) a polymeric layer containing olefinic unsaturation; and
b) a polymeric layer having active hydrogen atoms; wherein,
c) an adhesive layer is located between the layers derived from one or more compounds having one or more nitrile oxide moieties;
wherein a portion of the nitrile oxide moieties, or derivatives thereof, is reacted with olefinic unsaturation of layer a), the active hydrogen atoms of layer b) or both.
In another embodiment the invention is a process for the preparation of such a laminate which comprises
i. contacting one or more layers of one or both of a) a polymeric layer containing olefinic unsaturation; and b) a polymeric layer having active hydrogen atoms; wherein c) an adhesive layer derived from one or more compounds having nitrile oxide moieties is located between the two layers; and
ii. heating the contacted layers to a temperature and under conditions such that the nitrile oxide moieties, or derivatives thereof react with one or both of the olefinic unsaturation of layer a) and the active hydrogen containing layer b).
The process of the invention allows relatively easy preparation of the laminates of the invention. The laminates exhibit properties attributable to the layers present. Such laminates are useful as tires, belts and hoses, for example.
One or more layers of the laminate of the invention can be a polymer layer containing olefinic unsaturation.
Any polymer having olefinic unsaturation which is capable of reacting with a nitrile oxide moiety can be used in this invention. Preferable polymers containing olefinic unsaturation include rubber compositions, styrene-butyl rubber compositions, neoprene, ethylene-propylene terpolymers (prepared from ethylene-propylene-diene monomers, EPDM), monovinylidene aromatic monomer-conjugated diene block copolymers (such as block copolymers of styrene with butadiene or isoprene), polybutadiene, polyisoprene polychloroprene and the like. More preferred polymers containing olefinic unsaturation include rubber compositions, styrene-butyl rubber compositions, neoprene, ethylene-propylene terpolymers, monovinylidene aromatic monomer-conjugated diene block copolymers. Most preferred are natural rubber compositions and styrene-butyl rubber compositions. In one embodiment this polymeric layer may comprise a blend of polymers which contains at least one polymer with olefinic unsaturation. Preferably the polymer containing olefinic unsaturation has the olefinic unsaturation at the terminus of the polymer chain, i.e. has terminal olefinic unsaturation.
The other polymer layer may comprise a polymer having active hydrogen atoms which are reactive with nitrile oxide moieties or derivatives of such moieties. An example of such a derivative is an isocyanate moiety formed by the rearrangement of a nitrile oxide. For the purposes of this invention, an active hydrogen moiety refers to a moiety containing a hydrogen atom which, because of its position in the molecule, displays significant activity according to the Zerewitnoff test described by Wohler in the Journal of the American Chemical Society, Vol. 49, p. 3181 (1927). Illustrative of such active hydrogen moieties are xe2x80x94COOH, xe2x80x94OH, xe2x80x94NH2, xe2x80x94NHxe2x80x94, xe2x80x94CONH2, xe2x80x94SH, xe2x80x94COCH2COxe2x80x94, xe2x80x94NHCONHxe2x80x94, xe2x80x94OCONH and xe2x80x94CONHxe2x80x94. Typical active hydrogen containing polymeric layers include polyurethanes having residual active hydrogen containing moieties, polyols, polyamines, polymercaptans polyacids, polymers derived from acrylics and methacrylics, and styrene-acrylate based random copolymers. Suitable Imino-functional compounds are those which have at least one terminal imino group per molecule, such as are described, for example, in U.S. Pat. No. 4,910,279, which is hereby incorporated by reference in its entirety. Preferably, the active hydrogen containing polymer has hydroxyl, amino, mercapto, carboxylic acid, urethane, urea, carbamate moieties, or a mixture thereof and more preferably amino moieties, hydroxy moieties or a mixture thereof. Preferably, the active hydrogen containing polymer is a polyurethane having residual active hydrogen containing moieties or a polyol such as a polyether or polyester polyol. The polymer containing active hydrogen containing moieties may be blended with other polymers or additives. Preferably such polymers are found in a solid form and are elastomeric or plastic in nature.
Suitable polyols useful include, for example, polyether polyols, polyester polyols, poly(alkylene carbonate)polyols, hydroxyl-containing polythioethers, polymer polyols, and mixtures thereof. Polyether polyols are well-known in the art and include, for example, polyoxyethylene, polyoxypropylene, polyoxybutylene, and polytetramethylene ether diols and triols which are prepared by reacting an unsubstituted or halogen- or aromatic-substituted alkylene oxide with an initiator compound containing two or more active hydrogen groups such as water, ammonia, a polyalcohol, or an amine. Such methods are described, for example, in U.S. Pat. Nos. 4,269,945; 4,218,543; and 4,374,210; which are hereby incorporated by reference in their entirety. In general, polyether polyols may be prepared by polymerizing alkylene oxides in the presence of an active hydrogen-containing initiator compound.
Preferable alkylene oxides include ethylene oxide, propylene oxide, butylene oxides, styrene oxide, epichlorohydrin, epibromohydrin, and mixtures thereof. Preferable initiator compounds include water, ethylene glycol, propylene glycol, butanediol, hexanediol, glycerin, trimethylol propane, pentaerythritol, hexanetriol, sorbitol, sucrose, hydroquinone, resorcinol, catechol, bisphenols, novolac resins, phosphoric acid, aliphatic and aromatic amines, and mixtures thereof.
Polyester polyols are also well-known in the art and may be prepared by reacting a polycarboxylic acid, or an ester or anhydride thereof with a polyhydric alcohol. Examples of preferable polycarboxylic acids include succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, maleic acid, trimellitic acid, fumaric acid and terephthalic acid. Examples of preferable anhydrides include phthalic acid anhydride, tetrahydrophthalic acid anhydride, hexahydrophthalic acid anhydride, tetrachlorophthalic acid anhydride, endomethylene tetrahydrophthalic acid anhydride, maleic acid anhydride and glutaric acid anhydride., Mixtures of the polycarboxylic acids, esters and/or anhydrides described herein may be used. Examples of preferable polyhydric alcohols include ethylene glycols, propane diols, butane diols, 1,6-hexanediol, 1,8-octanediol, neopentylglycol, glycerol, trimethylol propane, pentaerythritol, quinitol, mannitol, sorbitol, methyl glycoside, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycols, polypropylene glycols, and mixtures thereof.
The adhesive layer comprises one or more compounds containing one or more nitrile oxide moieties. The compounds having nitrile oxide moieties suitable for the practice of the present invention have hindered nitrile oxide moieties. Nitrile oxide moiety as used herein corresponds to the formula xe2x80x94CNO. In some embodiments the nitrile oxide containing compound may further contain other reactive groups such as active hydrogen containing groups as defined herein. In another embodiment the nitrile oxide containing compound may be a polynitrile oxide. The term xe2x80x9cpolynitrile oxidexe2x80x9d is used herein to refer to a compound containing two or more nitrile oxide moieties per molecule. Preferably the nitrile oxide moieties are bound to aromatic rings. It is to be understood that the term xe2x80x9caromaticxe2x80x9d includes heteroaromatic moieties such as pyridines, furans, thiophenes, and the like.
Each nitrile oxide is adjacent to at least one substituent that is 1) unreactive with nitrile oxide and 2) non-interfering with the reaction between the nitrile oxide groups and unsaturated groups, preferably olefinically or acetylenically unsaturated groups and the reaction of nitrile oxide groups or derivatives thereof with active hydrogen containing compounds. Preferably, the polynitrile oxide forms less than 10 percent, more preferably less than 5 percent, and most preferably less than 1 percent dimers in 30 days at room temperature.
Preferably the poly-nitrile oxides of the invention comprise compounds having the structure: 
wherein each Rxe2x80x2 is independently C1-C12-alkyl, F. Cl, Br, I, Oxe2x80x94C1-C12-alkyl, or Sxe2x80x94C1-C12-alkyl; each Rxc2x0 is a substituent that does not spontaneously react with the nitrile oxide group; each nxe2x80x2 is independently 0, 1, or 2; nxe2x80x3 is an integer greater than 1; each Xxe2x80x2 is independently a bond or a connecting group; and Yxe2x80x2 is a polyvalent radical containing an ether, ester, amide, amine, carbonate, ketone, urethane, Arleen, or thioether moiety; or each Xxe2x80x2 and Yxe2x80x2 together are a bond connecting the benzene rings.
Examples of hindered aromatic polynitrile oxides include 
where R1, R2, and R3, and R4 are each independently H, R, halo, SH, SR, SOR, SO2R, hydroxy, or OR, with the proviso that at least one of R1, R21 R3, and R4 that is adjacent to a nitrile oxide group is not H; R5, R6, R7, and R8 are each independently H, R, halo, Sxe2x80x94H, SR, SOR, SO2R, hydroxy, or OR, wherein R is a C1-C12 linear, branched, or cyclic alkyl group, preferably a C1-C4 linear or branched alkyl group, more preferably ethyl or methyl; or R5 and R6, or R7 and R8, together with the carbon atoms to which they are attached, form a benzene ring, wherein at least one of R5 or R7 is not H, and at least one of R6 or R8 is not H; i is 2 or 3; m and n are each 0, 1, or 2, and n+mxe2x89xa72, preferably 2 or 3.
Other examples of hindered aromatic polynitrile oxides include compounds represented by the following structures: 
where R9, R10, R11, and R12 are each independently H, R, halo, SH, SR, SOR, SO2R, hydroxy, or OR with the proviso that at least one of R9 and R11 is not H when a nitrile oxide group is adjacent to both R9 and R11, and at least one of R10 and R12 is not H when a nitrile oxide group is adjacent to both R10 and R12; m, p, and r are each 0, 1, or 2, and p+rxe2x89xa72; X is CH2, C(R)2, carbonyl, O, S, SO, SO2, NH, SO2NH, SO2NR, or NR; t is 1, 2 or 3 and u is 0, 1, 2, or 3; and t+uxe2x89xa72; Y is a bond, CH2, C(R)2, carbonyl, O S, SO, SO2, NH, NR, 9,9xe2x80x2-fluoreno, or phenylene.
Examples of specific hindered aromatic polynitrile oxides that are suitable for the practice of the present invention include the following compounds: 
Stable aliphatic or cycloaliphatic polynitrile oxides can be prepared from a suitably functionalized aliphatic or cycloaliphatic polyaldehyde. The polyaldehyde can then be reacted with hydroxylamine to form the polyaldoxime, which can then be treated with bleach and caustic to form the desired aliphatic polynitrile oxide.
A suitably functionalized aromatic mononitrile oxide or monoaldehyde can be used to prepare a polynitrile oxide represented by the following formula: 
wherein each Rxe2x80x2 is independently C1-C12-alkyl, F, Cl, Br, I, Oxe2x80x94C1-C12-alkyl, or Sxe2x80x94C1-C12-alkyl; more preferably ethyl, methyl, n-propyl, isopropyl, n-butyl, isobutyl, methoxy, ethoxy; most preferably ethyl, methyl, or methoxy; each Rxc2x0 is a substituent that does not spontaneously react with the nitrile oxide group, preferably ethyl, methyl, n-propyl, isopropyl, n-butyl, isobutyl, methoxy, ethoxy, F, Cl, Br, or I; each nxe2x80x2 is independently 0, 1, or 2; nxe2x80x2 is an integer greater than 1, preferably 2, 3, or 4, more preferably 2 or 3, and most preferably 2; each Xxe2x80x2 is independently a bond or a connecting group such as an alkylene, cycloalkylene, or arylene group, more preferably a bond, a methylene group, or a phenylene group; and Yxe2x80x2 is a polyvalent radical, preferably a divalent radical, containing an ether, ester, amide, carbonate, ketone, urethane, arylene, or thioether group; or each Xxe2x80x2 and Yxe2x80x2 together are a bond connecting the benzene rings.
Suitably functionalized hindered aromatic mononitrile oxides or monoaldehydes preferably include 2,6-disubstituted benzonitrile oxides or benzaldehydes having an ester, acetate, hydroxy, epoxy, fluorine, chlorine, bromine, or iodine group connected directly to the benzene ring or indirectly through a connecting group. Preferably, the suitably functionalized 2,6-disubstituted benzonitrile oxide or benzaldehydes is represented by the following structure: 
where Rxe2x80x2, Rxc2x0, Xxe2x80x2, and nxe2x80x2 are previously defined; Q is xe2x80x94Cxe2x89xa1N30 Oxe2x80x94 or xe2x80x94CHO; and Zxe2x80x2 is an ester, acetate, amine, hydroxy, epoxy, amide, keto, aldehyde, fluorine, chlorine, bromine, or iodine group.
For example, 3-hydroxymethyl-2,4,6-trimethylbenzonitrile oxide or its corresponding benzaldehyde precursor can be: (a) transesterified with a diester or condensed with a diacid chloride to form a dinitrile oxide diester; (b) reacted with phosgene to form a dinitrile oxide containing a carbonate group; (c) reacted with a diisocyanate to form a dinitrile oxide containing urethane groups; (d) reacted with a dibenzyl chloride to form a dinitrile oxide containing two ether groups; (e) reacted with a diglycidyl ether to form a dinitrile oxide containing ether groups and hydroxy groups; and (f) reacted with an acid to form a difulmido dibenzyl ether.
Similarly, the suitably functionalized hindered aromatic nitrile oxide can be reacted with a second suitably functionalized hindered aromatic nitrile oxide to form a dinitrile oxide. For example, 3-hydroxymethyl-2,4,6-trimethylbenzonitrile oxide can be reacted with 3-chloromethyl-2,6-dimethylbenzene nitrile oxide to form a bis(nitrile oxide) dimethyl ether.
Polynitrile oxides having a functionality of greater than 2 (for example, a trinitrile oxide) can readily be prepared by reacting a dinitrile oxide with a compound having more than 2 unsaturated sites. For example, 2,4,6-triethylbenzene-1,3-dinitrile oxide can be reacted with trimethylol propane triacrylate to form the following trinitrile oxide: 
In another embodiment of the invention a cycloaliphatic nitrile oxide represented by the formula may be used in the invention: 
wherein R13 and each R14 are independently hydrogen, C1-Cl2 alkyl, or halo; x2 and X3 are each independently halo, hydroxyl, or together with the carbon atoms to which they are attached, form an epoxy group, preferably with the proviso that at least one of X2 and X3 is not halo; and n is 1 or 2, preferably 2. Preferably, each R14 is independently hydrogen, methyl, ethyl, chloro, or bromo; more preferably ethyl or methyl, and most preferably methyl. Preferably, R13 is hydrogen, methyl, or ethyl, more preferably hydrogen. Preferably, X2 and X3 are each independently hydroxy, chloro, bromo, or together with the carbon atoms to which they are attached form an epoxy group. More preferably, one of X2 and X3 is chloro, and the other of X2 and X3 is hydroxy, or X2 and X3 together with the carbon atoms to which they are attached form an epoxy group.
The nitrile oxide adhesive can be contacted with the polymeric layers neat, in a solvent or dispersant. The use of a solvent or a dispersant is preferred to enhance wet out of the adhesive layer on the surfaces of the polymeric layers. Any solvent or dispersant which dissolves or disperses the nitrile oxide and does not degrade the polymeric layers may be used. Preferably the solvent or dispersant is volatile at the conditions at which the adhesive reacts with the layers. Preferably the solvents or dispersants do not contain reactive moieties which interfere with the ability of the nitrile oxide to perform the desired function. Preferable solvents include haloalkanes and cyclic ethers. More preferred solvents include methylene chloride and dioxane. It is preferable to use water as a dispersant for the nitrile oxide. The nitrile oxide is dissolved or dispersed in a solvent at as high a solids level as possible to achieve the desired results. Preferably the solids level is about 20 percent by weight or greater, more preferably about 30 percent by weight or greater, even more preferably about 40 percent by weight or greater and most preferably 50 percent by weight or greater. Preferably the solids level is 70 percent by weight or less and more preferably 60 percent by weight or less.
The laminate structures of the invention are prepared by contacting the polymeric layers at the point where the layers are to be bonded. The polymeric layers to be contacted can be either selected from polymers containing olefinic unsaturation or polymers containing active hydrogen atoms or both. The nitrile oxide and the polymeric layers can be contacted in any sequence. Preferably the polymeric layers contacted comprise at least one polymeric layer containing olefinic unsaturation and at least one layer comprising a polymer containing active hydrogen atoms. Preferably the nitrile oxide is contacted with the polymer containing active hydrogen atoms before being contacted with the polymeric layer containing olefinic unsaturation because the nitrile oxide reacts much faster at ambient conditions with the latter than the former. Thereafter the contacted layers are exposed to temperatures at which the nitrile oxide moieties are reactive with the substrate layers, such as the active hydrogen containing moieties Preferably the contacted layers are exposed to temperatures of 80xc2x0 C. or greater, more preferably 100xc2x0 C. or greater and most preferably 150xc2x0 C. or greater. The upper limit on the temperature to which the layers are exposed after contacting is that temperature at which one or more of the polymeric layers undergo phase transition. Preferably the layers are exposed to temperatures of 200xc2x0 C. or less, more preferably 180xc2x0 C. or less and most preferably 170xc2x0 C. or less. Preferably the layers are subjected to pressure to improve the wet out of the adhesive layer to the contacted areas. Pressure is typically applied by mechanical means, such as by a press. Preferably the pressure applied is 5000 psi (34.5 mPa) or greater, more preferably 10,000 psi (79 mPa)or greater and most preferably 20,000 psi (158 mPa) or greater. Preferably the pressure applied is 50,000 psi (345 mPa) or less, more preferably 30,000 psi (237 mPa)or less and most preferably 25,000 psi (172 mPa) or less. The layers are exposed to the temperatures and applied pressures for a time sufficient to result in the reaction of nitrile oxide moieties, or derivatives thereof, with both polymeric layers such that the layers are bound together. Preferably such time is about 1 minute or greater and more preferably about 10 minutes or greater. Preferably such time is about 30 minutes or less and more preferably about 20 minutes or less.
It may be desirable to clean the surfaces of the polymeric layers to remove impurities or debris from the surfaces prior to the contacting. Such cleaning can be performed using techniques well known in the art. Preferably the surfaces are cleaned with a commmon solvent which does not degrade the surface cleaned. Preferable solvents include chlorinated alkanes, such as methylene chloride; ketones, such as acetone; aromatic hydrocarbons, such as benzene and toluene; lower alkanols, such as methanol, ethanol, isopropanol; cyclic ethers, such as dioxane; and the like.
In a preferred embodiment one polymeric layer is a polyurethane and the other layer is an uncured natural rubber composition. In this embodiment the layers are contacted and then subjected to the normal rubber vulcanization process. During the vulcanization process the polynitrile oxide reacts to adhere the two surfaces together.
The layers of the laminates can comprise any shape or thickness desired. The shapes and thicknesses of the layers are not an essential part of the invention.
The laminates exhibit good adhesion strengths. Preferably the laminates exhibit peel strengths, according to ASTM test No. D-413, of 11 pounds or greater and more preferably 13 pounds or greater.